Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $86.25   13.320%   $97.7385   $97.74   $97.75   $97.70  
  Purchase #2 $206.59   9.483%   $226.1809   $226.18   $226.20   $226.20  
  Purchase #3 $250.64   9.327%   $274.0172   $274.02   $274.00   $274.00  
  Purchase #4 $156.78   13.186%   $177.453   $177.45   $177.45   $177.50  
  Purchase #5 $49.42   7.239%   $52.9975   $53.00   $53.00   $53.00  
  Purchase #6 $234.38   5.385%   $247.0014   $247.00   $247.00   $247.00  
  Purchase #7 $178.37   5.121%   $187.5043   $187.50   $187.50   $187.50  
  7 purchase totals = $1,162.43       $1,262.8928   $1,262.89   $1,262.90   $1,262.90